The present invention is directed to a system for completing multiple hydrocarbon wells. More particularly, the invention is directed to a system and method for guiding a drill string during the drilling of multiple well bores in a side-by-side wellhead system.
In the oil and gas industry, side-by-side (xe2x80x9cSXSxe2x80x9d) wellhead systems, or multiple completion systems, are commonly used to drill and complete a number of hydrocarbon wells from within a single conductor housing. In such systems, multiple casing strings are run through the same conductor housing in order to reduce cost and space requirements. As shown in FIG. 1, a prior art SXS wellhead system may comprise a drive pipe housing A which is welded to the top of a conductor housing B, two or more casing strings C which are each suspended from the drive pipe housing, and a base plate D which is bolted to the top of the drive pipe housing. In this example, the well on the right is covered by an abandonment cap E, and a wellhead F is installed in the well on the left. In the drilling mode of operation of the SXS wellhead system, a drilling riser G may be bolted to the top of the wellhead F or connected directly to the base plate D.
One difficulty with SXS wellhead systems arises in the need to align and guide the drill string while drilling the well bores for the individual casing strings. If the first well bore is drilled too close to the center of the conductor housing, insufficient space will exist for the remaining well bores. One solution to this problem is disclosed in U.S. Pat. No. 6,142,235 to Monjure et al., which teaches using a permanently installed drilling guidance device in the conductor housing. However, this guidance device must be specially fabricated for each specific application, and this can be both costly and time consuming. Moreover, the guidance device must be permanently installed in the conductor housing, which requires that the cost for each guidance device be born for each SXS completion.
These and other disadvantages in the prior art are addressed by providing a system and method for drilling a plurality of well bores through a single conductor housing. The method comprises providing a base plate which includes at least first and second well slots that extend therethrough, supporting the base plate on the conductor housing, suspending a temporary casing string from the first well slot, drilling a first well bore through the second well slot, removing the temporary casing string from the first well slot, and then drilling a second well bore through the first well slot.
In accordance with one embodiment of the invention the diameter of the temporary casing string is larger than the diameter of a casing string which is subsequently suspended in the first well slot during completion of a well through the second well bore. In accordance with another embodiment of the invention, the temporary casing string is suspended from an offset casing hanger. Furthermore, individual lengths of the temporary casing string may be connected together by connector collars which have a larger diameter than the diameter of the temporary casing string.
Thus, the present invention comprises an economical method for guiding a drill string during the drilling of individual well bores in an SXS or multiple completion wellhead system. Since the diameter of the temporary casing string is larger than that of a subsequently installed casing string, sufficient room will exist after drilling the first well bore to drill the remaining well bores. In addition, because the temporary casing string is suspended from an offset casing hanger, the diameter of the temporary casing string can be significantly larger than the diameter of the subsequently installed casing string. Furthermore, after all the well bores have been drilled, the offset casing hanger and temporary casing string can be removed from the well. Consequently, these components can be reused on other multiple well completions.
These and other objects and advantages of the present invention will be made apparent from the following detailed description, with reference to the accompanying drawings. In the drawings, the same reference numbers are used to denote similar components in the various embodiments.